This invention relates to compositions for the production of building materials, particularly steam-cured building materials, and to methods of manufacturing such building materials.
To make steam-cured building materials usually mixtures of raw materials which contain silicic acid, such as for instance sand or slag, and calcareous binding agents, such as quick lime and/or cement are used, the height ratio of SiO.sub.2 containing components generally being between 90 to 10 and 65 to 35, preferably 80 to 20. After a forming process, these mixtures are cured in autoclaves with steam at elevated pressure and elevated temperature, respectively. Under these conditions, the silicic acid and the binding agents, especially the CaO-components of the binding agents dissolve and react while calcium hydro-silicates (CSH-phases) form. The latter act as binding agents in the steam-cured building material and provides the material its mechanical strength.
To increase reactivity during the autoclave treatment, not just the binding agents but also the siliceous components in the initial mixtures for the steam-cured building materials are finely ground. For instance, sand which is used for making gas concrete is thus ground to less 100 .mu.m. Any further comminution is economically prohibitive, and besides, the degree of fineness is limited due to the grinding means in use.
In gas concrete mixtures attempts have been made to use reactive silicic acids which are very fine to begin with. However, natural and industrial products of that kind are very expensive and not sufficiently uniform in their composition. Furthermore, they are generally not available in an acceptable quality containing too many components which render them unsuitable for the autoclave process.
Another disadvantage is that the fine silicic acid binds water. Thus, the viscosity of a water-containing mixture increases so strongly that, for instance, pumpability is reduced and the rising process of a gas concrete mixture may be incomplete. The stiffened mass gets too brittle and cannot be cut by conventional wire saws.
The object of the invention is therefore to create a mixture of lime and silicic acid components as well as a method, suitable for making building material, particularly for making steam-cured building materials, using finely divided silicic acids but without the aforementioned disadvantages.